Master cylinder with fluid-volume compensating valve in piston



y 3 A E. MILLER 2,638,748

MASTER CYLINDER WITH FLUID-VOLUME COMPENSATING VALVE IN PISTON Filed Aug. 13, 1948 2 Sheets-Sheet l Mm INVENTOR.

May 19, 1953 A. E. MILLER 2,633,748

MASTER CYLINDER WITH FLUID-VOLUME COMPENSATING VALVE IN PISTON 2 Sheets-Sheet 2 Filed Aug. 13, 1948 R r M M m Z r we m l R M NE 5 T n N M6 4 0 RA AP LM R Y T In-III nul-llluin w Patented May 19, 1953 MASTER CYLINDER WITH FLUID-VQLUME COMPENSATING VALVE I N PISTON Arthur E. Miller, Kenmore, N. Y., assignor to The Scott Aviation Corporation, Lancasten'NY;

Application August 13, 1948, Serial No. 44,17?

This invention relates to a master cylinder, i. e.. to an instrument for converting a mechanical force acting in one direction into fluid pressure, with means for returning the mechanical parts .to their original position and thereby releasing the fluid pressure when said mechanical force is removed. Master cylinders are commonly used to actuate vehicle and airplane brakes, fluid clutches and work holding vices, and for other similar purposes.

The principal object of the present invention is to provide a master cylinder which will have a long life of useiulness'by theelimination of the usual vent port of the cylinder which causes rapid wear in the packing of the usual piston, particularly when the brake shoe clearance is either zero (as in the Goodyear brake) or is close to zero as in most airplane brakes where the brake clearance is very small. A further. object of the invention is to accomplish this result with a master cylinder which is light and compact and is inexpensive to manufacture. Still further objects of the invention are to provide a master cylinder in which, in very simple manner, the fluid pressure may be maintained when the brake pedal pressure is released, and in which the level of the brake fluid in the master cylinder may be easily checked visually. .Other collateral objects and advantages of the invention are disclosed in detail in the following specification and appended drawings, wherein:

Fig. 1 is a diminutive side elevation of one form of my improved master cylinder.

Fig. 2 is a vertical, longitudinal section through this master cylinder, taken on line 2-2, Fig. 1.

Fig. 3 is a horizontal section, on a, smaller scale than that used in Fig. 2, of this master cylinder, taken on line 33, Fig. 1.

Fig. 4 is a horizontal section through the lower part of this master cylinder, taken on line 46, Fig.2.

Fig. 5 is a vertical, longitudinal section through a modified form of the invention.

Fig. 6 is a horizontal section thereof, on a reduced scale, taken on line 6- 5, Fig. 5.

Similar characters of reference indicate like parts in the several figures of the drawings.

First sheet (Figs. 1-4) Welded at it to the lower end of the cylinder I l of the master cylinder is a plug it which seals the lower end of said cylinder and is provided with 3, lug 13 provided with a pivot hole it which enable the entire assembly of the master cylinder to be pivotally mounted on the chassis of T'Claims. (c1. 60--54;6)

an automobile or airplane or to any other desired stationary base, in the usual and well known manner.

Welded at It to "the lower end or said cylinder is a nipple l6 which is suitably coupled or tubularly connected to the usual fluid conduits (not shown) which convey the fluid to and from the hydraulic brake or other hydraulic mechanism which is to be actuated. The cylinder is part0 rated at I! to allow the iluid to pass from the in= terior of the cylinder H into and out from said nipple I6.

Slidably disposed within the cylinder H is a piston [8 which is provided with a V type of annular acking constructed of synthetic rubber or like soft packing material. This piston is adapted to be actuated in a downward direction by a plunger 21 which is provided at its upper ens with an adjustable, threaded driving head 22 provided with a pivot hole 23 which is adapted to be connected in the usual and well known manner, through suitable linkages, etc., with the brake pedal. This driving head is held in its properly adjusted position by alock nut 24.

The lower end of the plunger 2| is tapered to form a conical valve 25 which is adapted to make fluid tight contact with a valve ring 26 having a valve seat 2 6a and preferably constructed of nylon or like material received within a suitable coaxially bored out recess 2! formed in the upper or rear face of the piston [8. The central upper part of said valve ring is annular'ly bored out to form a valve ring chamber 261). Th plunger 2! is suitablyguided within the cylinder I l by being received within the bore of a spacing bushing 28, the upper end of which, together with the upper end of the cylinder l I, is suitably received within an annular counterbore 30 formed in the lower end of a cylinder and reservoir head 3|. The upper end of the cylinder H is detachably secured to said head 31 by a set screw 29. The spacing bushing 28 is preferably, though not necessarily, a light push fit in the upper end of the cylinder ll.

Threaded onto the head 3| is a fluid reservoir 32 which is constructed of a suitable transparent material such as the plastic Lucite. Communication betweenthis reservoir 32 and the bore of the spacing bushing 28 is provided by one or more holes 33 drilled radially through the cylinder II and providing communication with an annular groove 34 formed in the lower periphery of the spacing bushing 28 and communicating through one or more radial holes or fluid passages 35 with the bore of the spacing bushing 28.

The lowermost end of the plunger 2| is provided with a stem or shank 36 which is longitudinally flattened at 31 and 31a and is externally threaded so as to adjustably receive the nut 38, which, when it has been adjusted, is pressed in at 40 and 40a so a to engage with the flattened faces 3! and 31a of the shank 3B and prevent any further rotation of the nut 38 after the master cylinder has been adjusted and assembled. The periphery of this nut 38 is of square or hexagonal shape so as to allow fluid to freely pas upward or downward past its peripheral faces. Communication past the lower face of the piston I8 is provided by one or more radial grooves 4|, and communication to or from the valve ring chamber 26a is provided by the flattened faces 31, 31a of the shank 36 of the plunger 2|.

In the fully retracted position of the master cylinders shown in the drawings, the nut 38 (Figs. 1-4) is being pressed upwardly forceably by a relatively heavy compression spring 42. This, concomitantly, forceably pushes upwardly the piston l8 against the lower end of the spacing bushing 28. But the nut 38 is so adjusted that when the piston H! ha thus been brought to a halt, the plunger 2| is moved a slight distance further so as to unseat the valve seat 25 of the plunger 2| from the valve seat 26a of the valve ring. Thus, when the master cylinder is not in use, there is provided a free communication between the reservoir 32 and the nipple l6 and thereby the brake actuating mechanism which is tubularly connected with said nipple. Hence any contraction or expansion of the fluid in the brake actuating mechanism, due to ambient thermal fluctuations is compensated for,'without any undue change in fluid pressure in the brake line, by permitting the fluid to move up into or out of the reservoir 32.

It has been found very desirable to ensure a prompt closing of the valve 25 just as soon as the plunger has moved downwardly a very short distance. To effect this result the increase in the fluid pressure in the region below the piston |8 has been found to be insuflicient to definitely attain the desired objective, because the pressure built up at the start of the downstroke of the plunger 2| is relatively small. In the present invention an annular spring washer 43 surrounds the shank 35 and is interposed between the lower or front face of the piston l3 and the upper or rear face of the nut 38. This spring washer 43 is much weaker than the coiled compression spring 42 but is sufficiently strong to move the valve 25 of the plunger 2| towards the valve seat 26a (and hence close the valve) whenever it (the spring washer) is not being opposed by said compression spring 42. In Fig. 2 the piston 8 is shown fully retracted, and in this position the spring washer 43 is squashed flat by the compression spring 42. However, when the plunger 2| is forced downwardly from the position of Fig. 2 and against the resistance of said compression spring 42, the spring washer 43 firmly holds up the piston l8 against the bottom end of the spacing bushing 28 until the valve 25 has made a firm, fluid-tight contact with the valve seat 2 6a. Further downward movement of the plunger 2| causes the piston |8 to be moved bodily with it.

By this construction a very slight downward movement of the plunger from the retracted position of Fig. 2 instantly and definitely closes the valve 25, irrespective of whether or not any appreciable pressure has been built up in the lower part of the cylinder II. This is, of course, particularly important when the plunger 2| is depressed at a relatively slow rate of speed such as occurs when the brakes are applied very gently.

As the reservoir 32 is constructed of a plastic material such as Lucite, its fluid-tight connection with the periphery of the cylinder II cannot be of conventional form. In the present invention this connection is elfected by thickening the lower end of the reservoir and forming therein an annular groove 44 to receive an 0 ring 45. This results in an inexpensive joint which is both adequately fluid-tight and readily detachable.

Also, the reservoir, being constructed of transparent material, the amount of fluid contained therein may be readily ascertained visually.

To scrape off fluid from the plunger 2| as it moves upwardly to the retracted position of Fig. 2, an upper O ring 46 is arranged in the reservoir head 3|.

It is sometimes desirable to lock the brakes without continuing to exert pressure on the brake pedal. This is effected by the provision of a tilt lever 41 which somewhat loosely embraces the plunger 2| in the clutch hole 48 which is bevelled at its upper corner at 50 to facilitate the locking action. The inner end of said tilt lever 41 is loosely received within a socket 5| formed by an L shaped lug 52 integrally formed at the upper face of the reservoir head 3|. The action is as follows: The operator first depresses the plunger 2| as far as he desires. He then manually lifts the outer end 53 of the tilt lever 41 until the plunger 2| is cramped. He is then free to release his pressure on the plunger 2| without allowing the brakes to be released. When he desires to release the brakes, he first depresses the plunger 2| until the tilt lever 41 is uncramped from said plunger under the influence of compression spring 54 which resiliently urges the outer end 53 of the tilt lever downwardly through the intermediary of a retracting rod 55 provided with a head 55 at its upper end and a squashed out portion 57 at its lower end. When the plunger 2| has thus been uncramped, the operator merely releases his pressure on the plunger 2| and the tilt lever 41, under the influence of its spring 54, remains inoperative until the operator desires to again "lock the 1brakes by lifting the outer end 53 of said tilt ever.

Second sheet (Figs. 5 and 6) The construction of master cylinder shown in these figures is fundamentally similar to that in Figs. 1-4, with the following exceptions:

l. The entire piston I'8L is constructed of nylon or similar material.

2. The tilt lever 41L is urged towards its retracted position by an annular magnet 60 which also serves to hold the upper O ring 46L in place.

3. The sleeve 28L is not employed to guide the plunger 2|L but is used solely to limit upward movement of the piston |8L and its lower end instead of being drilled to furnish fluid passages, is pressed out at one or more places to form semicircular fiuid passages 35L.

I claim:

1. A master cylinder comprising: a cylinder; a piston having a valve seat; a plunger having a portion adapted to engage said valve seat when said plunger is advanced and also having a forwardly extending threaded shank flattened on one face; and a nut arranged on said shank forwardly of the piston, and adapted to be compressed so as to engage said flattened face of said 1 4. after said nut has been adjusted to allow the desired forward movement of the piston relatively to the plunger.

2. A master cylinder comprising: a head having a counterbore; a cylinder having its rear end received within said counterbore and secured to said head; a reservoir; a spacing bushing arranged within said rear end of said cylinder and provided with a bleed hole communicating with said reservoir; a plunger slidably disposed within the bore of said spacing bushing; and a piston slidably-arranged at the front end of said plunger and disposed within the bore of the cylinder.

3. A master cylinder comprising: a head having a counterhore; a cylinder having its rear end receivedfwithin said counterbore and secured to said head; a reservoir; a spacing bushing arranged ,within said rear end of said cylinder and provided with a peripheral bleed channel communicatfing with said reservoir and also provided with a bleed hole opening into said bleed channel; a plunged slidably arranged within the bore of said spacing bushing; and a piston slidably arrangedfat the front end of said plunger and disposed within the bore of the cylinder.

4. A master cylinder comprising: a head; a reservoir; a cylinder connected at its rear end with said head and having a transfer aperture communicating with said reservoir; a spacing bushing arranged within said rear end of said cylinder and provided with a bleed hole communicating with said transfer aperture; a plunger slidably arranged within the bore of said spacing bushing; and a piston slidably arranged at the front end of said plunger in front of said spacing bushing and within the bore of the cylinder.

5. A master cylinder comprising: a head; a reservoir; a cylinder connected at its rear end with said head and having a transfer aperture communicating with said reservoir; a spacingbushing arranged within said rear end of said cylinder and provided with a peripheral fluid channel and a fluid passage both communicating with said transfer aperture; a plunger slidably arranged within the bore of said spacing bushing; and a piston slidably arranged at the front end of said plunger and disposed within the bore of the cylinder.

6. A master cylinder comprising: a head; a reservoir; a cylinder connected with said head; a spacing bushing in said cylinder; a plunger in said bushing and having a forwardly extending shank; a piston on said shank and in said cylinder; and means for limiting the forward movement of said piston relatively to the plunger.

7. A master cylinder comprising: a head; a reservoir; a cylinder connected with said head; a spacing bushing in said cylinder; a plunger in said bushing and having a forwardly extending threaded shank; a piston on said shank and in said cylinder; and having a radial groove on its front face; and a nut on said threaded shank and arranged forwardly of said piston.

ARTHUR E. MILLER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,997,100 Boughton Apr. 9, 1935 2,004,078 McDougall June 4, 1935 2,020,465 Hall Nov. 12, 1935 2,041,065 Hemphill May 19, 1936 2,060,846 Bowen Nov. 17, 1936 2,120,073 Majneri June: 7, 1938 2,152,345 Bowen Mar. 28, 1939 2,152,499 Rasmussen Mar. 28, 1939 2,219,336 Sauzedde Oct. 29, 1940 2,242,096 Thomas May 13, 1941 2,248,426 Fowler July 8, 1941 2,310,976 Masteller Feb. 16, 1943 2,326,116 Baldwin Aug. 10, 1943 2,447,142 Smith et a1. Aug. 17, 1948 2,541,312 Vogel Feb. 13, 1951 

